This invention relates to a semiconductor device, more particularly to a semiconductor device possessing an insulating film of high quality and the method for fabricating the same.
Conventionally, thermally oxidized films and nitrided oxide films formed on a semiconductor substrate were used as the gate oxide film for an MOS type semiconductor device or tunnel oxide film for an EEPROM semiconductor device.
In the gate insulation film of the conventional structure, however, hot carriers generated in the high electric field region due to the recent microminiaturization of semiconductors are injected into the gate insulating film. As a result of this injection, a shift of flat-band voltage and deterioration of electric characteristics due to an increase of interface state density are caused, in particular, fluctuations of threshold voltage occur in the ordinary superfine MOS, and fluctuations of potential beneath the gate in the writing state of signal "1" and in non-writing state are experienced in the EEPROM, which presents serious problem in the setting of operation margins or reliability of the device.
To solve these problems and also to obtain stabler gate insulating films, it has been attempted among some researchers to use nitrided oxide films instead of thermally oxidized ones, but practical materials have not been developed yet.